From U.S. Pat. No. 5,409,429 an auxiliary transmission is known, by virtue of which all-wheel drive can be engaged in case of need. For this, the auxiliary transmission has a controllable clutch and a distributor unit for the optional distribution of the drive torque to one or two drive output shafts of a vehicle. In addition, the auxiliary transmission is made with a reduction gear stage and a hydraulic pump.
However, a drawback of this is that the hydraulic pump is located after the reduction gear stage and the delivery performance of the pump varies markedly as a function of the engagement condition of the reduction gear stage, so that in order to guarantee the supply to the auxiliary transmission the hydraulic pump has to be made very large.
The purpose of the present invention is therefore to provide an auxiliary transmission of low total weight that can be adapted to various requirement profiles in a simple way and in which the drive power available for a hydraulic pump is at least approximately constant.